Nickel powder manufacturing method

ABSTRACT

Provided is a nickel powder manufacturing method capable of efficiently manufacturing a high-quality nickel powder using as little ammonium gas or ammonium water as possible. The nickel powder manufacturing method according to the present invention is characterized by comprising: a first step for generating a post-neutralization slurry including nickel hydroxide by mixing a nickel sulfate aqueous solution and a neutralizing agent; a second step for causing a complex-forming reaction by mixing an ammonium sulfate aqueous solution with the post-neutralization slurry and obtaining a post-complexation slurry including a nickel ammine complex aqueous solution; and a reducing step for obtaining a nickel powder and a post-reduction solution by contacting hydrogen gas with the nickel ammine complex aqueous solution. Further, it is preferable that a post-complexation solution obtained in the reduction step be repeatedly used as the ammonium sulfate aqueous solution to be added to the post-neutralization slurry.

TECHNICAL FIELD

The present invention relates to a nickel powder manufacturing method,and relates to a method for manufacturing nickel powder by obtaining anickel ammine complex aqueous solution from nickel hydroxide and thensubjecting the nickel ammine complex aqueous solution to a hydrogenreduction treatment.

BACKGROUND ART

A nickel ammine complex aqueous solution can be used as a useful rawmaterial, for example, by subjecting the nickel ammine complex aqueoussolution to hydrogen reduction, fine nickel powder can be obtained asdisclosed in Patent Document 1. Such a nickel ammine complex aqueoussolution can be obtained, for example, using ammonia gas or ammoniawater in a nickel sulfate aqueous solution.

In the method in which nickel powder is obtained by using, as a rawmaterial, a nickel ammine complex aqueous solution obtained from ammoniagas or ammonia water and subjecting the nickel ammine complex aqueoussolution to hydrogen reduction, sulfate radical generated simultaneouslywith the nickel powder is bonded to ammonia to generate an ammoniumsulfate aqueous solution. Therefore, if the sulfate radical of thegenerated ammonium sulfate aqueous solution is not discharged outsidethe system, a problem arises in that the balance of the liquid in thereaction system is not achieved or the sulfur grade of the nickel powderas a product increases.

As the method of carrying out the sulfate radical outside the system, inthe related art, there is known a method of separating and carrying outthe sulfate radical as crystal powder of ammonium sulfate using acrystallization method and newly adding ammonia to a reaction liquid, ora method of adding a neutralizing agent such as slaked lime or sodiumhydroxide to an ammonium sulfate aqueous solution to generate ammoniawater, gypsum, and a salt cake (sodium sulfate hydrate), discharging thesulfate radical outside the system in the form of gypsum and a saltcake, and recycling ammonia water in the system.

However, upon using those methods, problems arise in that investment forfacilities increases, and risk to natural environment or workingenvironment caused by ammonia that is a malodorous substance increases.Further, time and effort and cost for treating discharged watercontaining ammonia to be generated are not negligible.

For this reason, a method is demanded in which a nickel ammine complexaqueous solution is manufactured while the amount of ammonia used isreduced as much as possible and nickel powder is manufactured using thenickel ammine complex aqueous solution.

Patent Document 1: Japanese Unexamined Patent Application, PublicationNo. 2000-063916

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

The present invention is proposed in view of such circumstances, and anobject thereof is to provide a nickel powder manufacturing method bywhich a high-quality nickel powder can be efficiently manufactured usingas little ammonia gas or ammonia water as possible.

Means for Solving the Problems

The present inventors have conducted intensive studies in order to solvethe aforementioned problems. As a result, they have found that by usingan ammonium sulfate aqueous solution when a nickel ammine complex isobtained from nickel hydroxide, a high-quality nickel powder can beefficiently obtained while the amount of ammonia used is suppressed tothe minimum, thereby completing the present invention. Specifically, thepresent invention provides the followings.

(1) A first invention of the present invention is a nickel powdermanufacturing method, the method including: a first step for generatinga post-neutralization slurry containing nickel hydroxide by mixing anickel sulfate aqueous solution and a neutralizing agent; a second stepfor causing a complex-forming reaction by mixing an ammonium sulfateaqueous solution with the post-neutralization slurry obtained in thefirst step and obtaining a post-complexation slurry containing a nickelammine complex aqueous solution; and a reduction step for obtainingnickel powder and a post-reduction solution by bringing hydrogen gasinto contact with the nickel ammine complex aqueous solution obtained inthe second step.

(2) A second invention of the present invention is the nickel powdermanufacturing method in the first invention, in which in the secondstep, the post-reduction solution obtained in the reduction step is usedas the ammonium sulfate aqueous solution to be mixed with thepost-neutralization slurry.

(3) A third invention of the present invention is the nickel powdermanufacturing method in the first or second invention, the methodfurther including a third step for subjecting the post-complexationslurry obtained in the second step to solid-liquid separation into anickel ammine complex aqueous solution and a post-complexation sedimentand supplying the nickel ammine complex aqueous solution to thereduction step.

(4) A fourth invention of the present invention is the nickel powdermanufacturing method in any one of the first to third inventions, inwhich in the first step, slaked lime and/or sodium hydroxide is used asthe neutralizing agent.

(5) A fifth invention of the present invention is the nickel powdermanufacturing method in any one of the first to fourth inventions, inwhich in the reduction step, the nickel powder is obtained by addingammonia water to the nickel ammine complex aqueous solution and thenbringing the hydrogen gas into contact with the nickel ammine complexaqueous solution.

Effects of the Invention

According to the present invention, a high-quality nickel powder can beefficiently manufactured with the amount of ammonia used beingsuppressed to the minimum, and productivity can be improved in terms ofenvironment and cost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram illustrating an example of a flow of a nickelpowder manufacturing method.

FIG. 2 is a flow diagram illustrating a flow of the nickel powdermanufacturing method when ammonia water is added in a reduction step.

PREFERRED MODE FOR CARRYING OUT THE INVENTION

Hereinafter, a specific embodiment of the present invention will bedescribed in detail. Incidentally, the present invention is not limitedto the following embodiment, and various modifications can be madewithin the range that does not change the spirit of the presentinvention.

The nickel powder manufacturing method according to the presentinvention is a method for manufacturing nickel powder by adding aneutralizing agent to a nickel sulfate aqueous solution to generatenickel hydroxide, obtaining an aqueous solution of a nickel amminecomplex from the nickel hydroxide, and then subjecting the nickel amminecomplex to hydrogen reduction.

At this time, in the nickel powder manufacturing method according to thepresent invention, it is characterized in that when a nickel amminecomplex is obtained from nickel hydroxide, a complex-forming reaction ofnickel is generated using an ammonium sulfate aqueous solution.

Specifically, this nickel powder manufacturing method includes: a firststep for generating a post-neutralization slurry containing nickelhydroxide by mixing a nickel sulfate aqueous solution and a neutralizingagent; a second step for causing a complex-forming reaction by mixing anammonium sulfate aqueous solution with the post-neutralization slurryand obtaining a post-complexation slurry containing a nickel amminecomplex aqueous solution; and a reduction step for obtaining nickelpowder and a post-reduction solution by bringing hydrogen gas intocontact with the nickel ammine complex aqueous solution.

Further, as the ammonium sulfate aqueous solution used when a nickelammine complex is formed, it is preferable to use an ammonium sulfateaqueous solution generated by subjecting the nickel ammine complex tohydrogen reduction in the reduction step. In this way, by repeatedlyusing the ammonium sulfate aqueous solution obtained by the treatment inthe reduction step in the reaction of forming a nickel ammine complex inthe second step, nickel powder can be more efficiently manufactured.

In this way, by the nickel powder manufacturing method according to thepresent invention, a high-quality nickel powder can be manufacturedwhile the amount of ammonium used is suppressed to the minimum ascompared to the related art. Moreover, by forming a nickel amminecomplex repeatedly using the ammonium sulfate aqueous solution obtainedin the reduction step, nickel powder can be manufactured on the basis ofthe treatment that is effective in terms of cost and industrial aspect.

Hereinafter, the nickel powder manufacturing method according to thepresent invention will be described in more detail. FIG. 1 is a flowdiagram illustrating an example of a flow of a nickel powdermanufacturing method.

As illustrated in FIG. 1, the nickel powder manufacturing methodaccording to the present embodiment includes: a first step forgenerating nickel hydroxide by adding a neutralizing agent to a nickelsulfate aqueous solution; a second step for forming a nickel amminecomplex from the nickel hydroxide; a third step for solid-liquidseparating a nickel ammine complex aqueous solution from the obtainedslurry; and a reduction step for generating nickel powder by subjectingthe nickel ammine complex aqueous solution to hydrogen reduction.

[First Step]

In the first step, a post-neutralization slurry containing nickelhydroxide is generated by mixing a nickel sulfate aqueous solution and aneutralizing agent. Incidentally, the post-neutralization slurry is, forexample, a slurry obtained by mixing nickel hydroxide and a gypsumslurry in the case of using slaked lime as a neutralizing agent and aslurry of nickel hydroxide in the case of using sodium hydroxide as aneutralizing agent.

Specifically, in the first step, a certain amount of the nickel sulfateaqueous solution is charged, for example, in a neutralization reactiontank and a neutralizing agent is added thereto, so that the pH of thenickel sulfate aqueous solution is adjusted to, for example, about 7.8to 8.5, preferably about 8.0. By the neutralization treatment using theneutralizing agent, nickel hydroxide is generated from the nickelsulfate aqueous solution and a post-neutralization slurry containing thenickel hydroxide is obtained.

(Nickel Sulfate Aqueous Solution)

Herein, the nickel sulfate aqueous solution used in the raw material isnot particularly limited, but a sulfuric acid solution obtained byleaching nickel can be used.

For example, it is possible to use a nickel sulfate aqueous solutionobtained by dissolving a nickel-containing material such as anindustrial intermediate consisting of one or a plurality of mixturesselected from nickel and cobalt mixed sulfide, coarse nickel sulfate,nickel sulfide, and the like, or scraps of nickel metal, with sulfuricacid to obtain a nickel leachate, subjecting the nickel leachate to apurification step such as a solvent extraction method, an ion exchangemethod, or neutralization to remove impurity elements.

Incidentally, the concentration of nickel in the nickel sulfate aqueoussolution is roughly 100 g/L to 150 g/L and is preferably set to a valuearound 120 g/L, from the viewpoint that the treatment is performed in anappropriate facility scale by suppressing an excessively large increasein solubility or liquid amount.

(Neutralizing Agent)

As the neutralizing agent, slaked lime (calcium hydroxide) can be used.Incidentally, the slaked lime is preferably used in the form of aslurry. Specifically, as the slaked lime, commercially availableproducts for industrial use can be used, and there is no particularlimitation. For example, commercially available slaked lime is adjustedusing water to have a slurry concentration of about 150 g/L and used.

Incidentally, in the case of using a calcium compound as theneutralizing agent, although not limited to slaked lime, for example,calcium carbonate or the like can also be used.

Further, as the neutralizing agent, sodium hydroxide can also be used.As the sodium hydroxide, commercially available products for industrialuse can be used, and there is no particular limitation. Further, as thesodium hydroxide as the neutralizing agent, from the viewpoint of havingfavorable conveying properties and easily adjusting the added amount,the sodium hydroxide is preferably used in the form of an aqueoussolution.

Other than the sodium hydroxide, water-soluble alkali such as potassiumhydroxide, and soluble alkali such as magnesium hydroxide or magnesiumoxide may be used. These are preferable from the viewpoint that handlingis easier because, for example, time and effort for forming a slurry canbe reduced and the amount of sediment generated is reduced.

In the first step, the reaction temperature of the neutralizationreaction is preferably set to about 40° C. to 60° C. and more preferablyabout 50° C., and with this range, thermal energy for heating in theprevious or next step is not wasteful, and the treatment can be moreefficiently performed.

[Second Step]

In the second step, a complex-forming reaction of nickel is caused usingthe post-neutralization slurry containing nickel hydroxide obtained inthe first step, thereby obtaining a solution of a nickel ammine complex.At this time, it is characterized that an ammonium sulfate aqueoussolution is used at the time of the complex-forming reaction of nickel,and the ammonium sulfate aqueous solution is added to thepost-neutralization slurry to obtain a solution of a nickel sulfateammine complex as a post-complexation slurry.

In this way, by using the ammonium sulfate aqueous solution when anickel ammine complex is generated, as compared to the case of therelated art where the complex-forming reaction is performed usingammonia gas or ammonia water, facility cost and working environment canbe improved, and a high-quality nickel powder can be efficientlymanufactured.

Incidentally, the post-complexation slurry is a slurry obtained bymixing a nickel sulfate ammine complex and a gypsum slurry in the caseof using slaked lime as a neutralizing agent in the first step and is aslurry of a nickel sulfate ammine complex in the case of using sodiumhydroxide as a neutralizing agent.

As the ammonium sulfate aqueous solution, those having an ammoniumsulfate concentration of about 200 g/L to 500 g/L are preferably used,and those having an ammonium sulfate concentration of about 400 g/L aremore preferably used. In the case of an aqueous solution having anammonium sulfate concentration of less than 200 g/L, nickel hydroxide inthe post-neutralization slurry cannot be completely dissolved in somecases, and a double salt of nickel may be precipitated. Further, in thecase of an aqueous solution having a concentration of more than 500 g/L,ammonium sulfate may be precipitated beyond the solubility after thetreatment in the reduction step of the subsequent step.

The reaction temperature of the complex-forming reaction in the secondstep is preferably about 40° C. to 90° C. and more preferably about 60°C. to 80° C. When the reaction temperature is lower than 40° C., thereaction speed is slow, which is difficult to industrially apply; on theother hand, even when the reaction temperature is higher than 90° C.,the reaction speed is not changed, and the loss of energy increases.

Herein, in the second step, when the complex-forming reaction is causedusing the ammonium sulfate aqueous solution, it is preferable that anammonium sulfate aqueous solution as a post-reduction solution obtainedin the reduction step described later is recovered and repeatedly used.In this way, by repeatedly reusing the ammonium sulfate aqueous solutionobtained in the reduction step, nickel powder can be manufactured by thetreatment that is more effective in terms of cost and industrial aspect.

Incidentally, at the time of start-up of process or in a case where therepeatedly used amount is insufficient due to a change in ammoniabalance according to continuous operations, one newly prepared from aseparately prepared reagent or the like as described in the related artmay be complementarily used.

[Third Step]

A step for solid-liquid separating a post-complexation slurry containingthe nickel ammine complex aqueous solution generated by thecomplex-forming reaction in the second step can be provided as a thirdstep, although this is not essential aspect.

For example, in the case of using slaked lime as a neutralizing agent inthe first step, as described above, the post-complexation slurryobtained in the second step is a slurry composed of a solution having anickel sulfate ammine complex and a post-complexation sediment. Thepost-complexation sediment is a neutralized sediment mainly containing asulfate radical derived from nickel sulfate as a raw material, such asgypsum based on slaked lime as a neutralizing agent. Therefore, byproviding the step for subjecting the post-complexation slurry to asolid-liquid separation treatment as a third step, a nickel amminecomplex aqueous solution from which the sediment is separated andremoved can be recovered, and the nickel ammine complex aqueous solutionin which such impurities are reduced can be supplied to the next step.In this way, it can be suppressed that sulfur or the like is get intoand contained in the nickel powder generated in the reduction step, andthus quality can be further improved.

The method for solid-liquid separation is not particularly limited. Forexample, filtration under reduced pressure using a tank filter,filtration under pressure using a filter press, and the like areexemplified, and separation by decantation may be performed beforefiltration using those filters.

Incidentally, in the case of using soluble alkali such as sodiumhydroxide or magnesium oxide as a neutralizing agent in the first step,a neutralized sediment such as gypsum is not generated. Therefore, thethird step for the solid-liquid separation treatment is not necessarilyprovided. However, since hydroxide composed of other impurity componentsis generated by neutralization using those neutralizing agents in somecases, from the viewpoint of maintaining or improving the quality of thenickel powder generated in the reduction step, it is preferable that thesolid-liquid separation treatment is performed to reliably supply onlythe nickel ammine complex aqueous solution to the reduction step.

[Reduction Step]

In the reduction step, the hydrogen reduction is performed by bringinghydrogen gas into contact with the obtained nickel ammine complexaqueous solution, thereby generating nickel powder. Specifically, first,the nickel ammine complex aqueous solution is charged in a reactioncontainer such as a reaction container for high temperature and highpressure, hydrogen gas for reduction is continuously supplied under theconditions of a predetermined temperature and a predetermined pressureto cause hydrogen reduction, thereby generating a slurry composed of thenickel powder and the ammonium sulfate aqueous solution as apost-reduction solution.

The reaction temperature in the reduction step is not particularlylimited, but is preferably about 130° C. to 250° C. and more preferablyabout 150° C. to 200° C. When the reaction temperature is lower than130° C., reduction efficiency may be degraded; on the other hand, evenwhen the reaction temperature is higher than 250° C., the reaction isnot affected, and the loss of thermal energy increases.

Further, the pressure condition inside the reaction container at thetime of the reaction is not particularly limited, but is preferablyabout 1.0 MPa to 5.0 MPa and more preferably about 2.0 MPa to 4.0 MPa.When the internal pressure is less than 1.0 MPa, reduction efficiencymay be degraded; on the other hand, even when the internal pressure ismore than 5.0 MPa, the reaction is not affected, and the loss ofhydrogen gas increases.

Further, in the hydrogen reduction treatment in the reduction step, itis preferable to add the nickel powder as seed crystals to the nickelammine complex aqueous solution contained in the reaction container. Byperforming the hydrogen reduction treatment in a state of the seedcrystals being added in this way, the reduction rate to the metallicnickel can be increased, and the particle size of the nickel powder thusobtained can be controlled.

Specifically, as the nickel powder added as seed crystals, for example,those having an average particle size of about 0.1 μm to 300 μm can beused. Further, those having a particle size of about 10 μm to 200 μm aremore preferably used. When the particle size of the nickel powder asseed crystals is less than 0.1 μm, the nickel powder thus obtainedbecomes too fine, so that the effect of the nickel powder as seedcrystals may not be exhibited. On the other hand, when the particle sizeof the nickel powder as seed crystals is more than 300 μm, the nickelpowder becomes coarse, so that the nickel powder is likely to beeconomically disadvantaged.

Further, as the nickel powder as seed crystals, a commercially availablenickel powder can be used, and nickel powder chemically precipitated bya known method can be classified and used. Furthermore, the nickelpowder manufactured by the manufacturing method may be repeatedly used.Incidentally, the nickel powder as seed crystals may be continuouslysupplied to a reaction container by using a supply device such as aslurry pump along with the nickel ammine complex aqueous solution as araw material.

Further, in the hydrogen reduction treatment in the reduction step, itis preferable to add a dispersant to the nickel ammine complex aqueoussolution. By performing the hydrogen reduction treatment by adding adispersant in this way, the reduction rate to metallic nickel can beincreased, and the surface of nickel powder thus obtained can be furthersmoothed. Further, aggregation or the like is prevented, and thus nickelpowder having a nearly homogeneous particle size can be manufactured.

Specifically, the dispersant is not particularly limited, but a polymerhaving an anionic functional group such as sodium polyacrylate or apolymer having a non-ionic functional group such as polyethylene glycolor polyvinyl alcohol can be used.

Herein, in the hydrogen reduction treatment in the reduction step, it ispreferable to add ammonia water to the nickel ammine complex aqueoussolution. In this way, by adding ammonia water to the nickel amminecomplex aqueous solution and subjecting the aqueous solution to thehydrogen reduction treatment, the reduction rate of nickel can beincreased. Specifically, FIG. 2 is a flow diagram of a manufacturingmethod illustrating an aspect in which ammonia water is added to anickel ammine complex aqueous solution and the nickel ammine complexaqueous solution is subjected to a hydrogen reduction treatment.

It is known that when the nickel ammine complex aqueous solution issubjected to the reduction treatment by using hydrogen gas, the pH of areduced solution (post-reduction liquid) is gradually decreased. Thepresent inventors have found that, due to such a decrease in pH of thepost-reduction liquid, the generated nickel powder is dissolved again todecrease the nickel reduction rate. From this, by adding ammonia waterto the nickel ammine complex aqueous solution and then subjecting theaqueous solution to the hydrogen reduction treatment, a decrease in pHof the post-reduction liquid can be suppressed, and a decrease in nickelreduction rate, that is, a decrease in recovery amount of the nickelpowder can be suppressed.

Further, by setting the amount of ammonia water added to small, nickelpowder can be manufactured by an efficient treatment without time andeffort and cost being increased. Incidentally, it is preferable that theamount of ammonia water added is set such that the concentration ofammonia in the solution is, for example, about 1 g/L to 10 g/L. When theconcentration of ammonia in the solution is less than 1 g/L, the effectof suppressing a decrease in nickel powder recovery amount is small; onthe other hand, when the ammonia water is added at a rate exceeding 10g/L, the loss of the reagent is increased without the effect beingimproved any more.

(Regarding Taking Out of Nickel Powder)

The reacted slurry in the reaction container which is obtained in thereduction step is discharged, for example, to a depressurized tank andsubjected to solid-liquid separation, and thus the nickel powder isrecovered and an ammonium sulfate aqueous solution as a post-reductionsolution is taken out. The ammonium sulfate aqueous solution taken outhere is, as described above, preferably reused as the ammonium sulfateaqueous solution for the complex-forming reaction in the second step.Specifically, the taken-out ammonium sulfate aqueous solution iscirculated and added to the post-neutralization slurry.

In the related art, upon recovering nickel, nickel needs to be recoveredfrom an unreacted nickel ammine complex aqueous solution remaining inthe ammonium sulfate aqueous solution as a post-reduction solution.Therefore, at a stage prior to the recovery treatment of ammoniumsulfate or the treatment of recovering ammonia water from ammoniumsulfate, the treatment of recovering nickel has to be performed, andthus a problem arises in that facility cost or operation cost isincreased. On the other hand, by repeatedly using the total amount ofthe ammonium sulfate aqueous solution generated in the reduction step asa solution for complex-forming reaction in the second step, an operationof preparing a separate facility to recover nickel is not necessary,cost can be effectively reduced, and an efficient operation can beperformed.

EXAMPLES

Hereinafter, the present invention will be described in more detail bymeans of Examples and Comparative Examples, but the present invention isnot limited to the following Examples.

Example 1 (First Step)

A nickel oxide ore was subjected to acid leaching under a hightemperature and a high pressure by a known method, and then sulfuricacid was added to nickel sulfide obtained by subjecting a nickelleachate to a sulfuration treatment while the liquid temperature wasmaintained to 50° C. such that the nickel sulfide was dissolved to havea nickel concentration of 120 g/L, thereby obtaining a nickel sulfateaqueous solution. 1 L of the obtained nickel sulfate aqueous solutionwas separated, a slaked lime slurry having a slurry concentration of 150g/L was added thereto, and the resultant slurry was stirred for 60minutes and maintained such that the pH of the slurry would be 8.0,thereby obtaining a post-neutralization slurry. Incidentally, the finalamount of the slaked lime slurry added was 1.26 L.

(Second Step)

1.0 L of ammonium sulfate aqueous solution having a concentration of1240 g/L was added to the post-neutralization slurry containing nickelhydroxide generated in the first step. Incidentally, the concentrationof ammonium sulfate added in the post-neutralization slurry was 400 g/L.Subsequently, stirring was continued for 1 hour while the temperature ofthe aqueous solution was maintained to 80° C., and the nickel hydroxideand ammonium sulfate in the aqueous solution was reacted with each otherto generate a nickel ammine complex. According to this, apost-complexation slurry containing the nickel ammine complex and agypsum slurry was obtained.

(Third Step)

Next, the post-complexation slurry obtained in the second step wassolid-liquid separated using Nutsche and filter paper. According tothis, 2.9 L of nickel ammine complex aqueous solution having a nickelconcentration of 41 g/L was obtained as a filtrate.

(Reduction Step)

Next, 1 L of the obtained nickel ammine complex aqueous solution wascharged in a high temperature and high pressure reaction container, 40 gof nickel powder separately prepared as seed crystals and sodiumpolyacrylate as a dispersant were added such that the concentrationwould be 0.17 g/L, the temperature was increased to 185° C., and thereaction was performed for 1 hour by supplying hydrogen gas understirring under the condition that the internal pressure was maintainedto 3.5 MPa.

After completion of the reaction, the reacted slurry was taken out fromthe reaction container, the generated nickel powder was recovered bysolid-liquid separation, and the quantity thereof was measured. As aresult, it was confirmed that 90% of nickel contained in the suppliednickel ammine complex aqueous solution can be recovered as a metallicnickel powder.

Example 2 (First Step)

Similarly to Example 1, 1 L of nickel sulfate aqueous solution which isdissolved under the condition of a reaction temperature of 50° C. suchthat the nickel concentration would be 120 g/L was prepared. Then, 810mL of sodium hydroxide aqueous solution having a concentration of 200g/L was added to the nickel sulfate aqueous solution and mixed to obtaina post-neutralization slurry having a pH of 8.2.

(Second Step)

To the post-neutralization slurry containing nickel hydroxide generatedin the first step, 400 g of ammonium sulfate aqueous solution and 207 gof nickel hydroxide (in terms of Dry) obtained in the first step andwater were added so that the total liquid amount was adjusted to 1000mL. Subsequently, while the temperature of the aqueous solution afterthe adjustment was maintained to 80° C., stirring was continued for 1hour, thereby generating a nickel ammine complex aqueous solution in astate in which the total amount of nickel hydroxide and ammonium sulfatewas dissolved.

(Third Step)

In the aforementioned first step, since sodium hydroxide was used as aneutralizing agent, sediment was not generated in the nickel amminecomplex aqueous solution discharged from the second step. Therefore, thenickel ammine complex aqueous solution was transferred to the reductionstep without providing the third step in which the solid-liquidseparation is performed.

(Reduction Step)

Next, 1 L of the obtained nickel ammine complex aqueous solution wascharged in a high temperature and high pressure reaction container, 40 gof nickel powder separately prepared as seed crystals and sodiumpolyacrylate as a dispersant were added such that the concentrationwould be 0.17 g/L, the temperature was increased to 185° C., and thereaction was performed for 1 hour by supplying hydrogen gas understirring under the condition that the internal pressure was maintainedto 3.5 MPa.

After completion of the reaction, the reacted slurry was taken out fromthe reaction container, the generated nickel powder was recovered bysolid-liquid separation, and the quantity thereof was measured. As aresult, it was confirmed that 95% of nickel contained in the suppliednickel ammine complex aqueous solution can be recovered as a metallicnickel powder.

Example 3

The treatment from the first step to the third step was performed usingthe same method as in Example 1 to obtain 1 L of nickel ammine complexaqueous solution.

Subsequently, 1 L of the obtained nickel ammine complex aqueous solutionwas charged in a high temperature and high pressure reaction container,and similarly to the reduction step of Example 1, the reaction wasperformed for 1 hour by supplying hydrogen gas under the conditionsincluding a temperature of 185° C. and an internal pressure of 3.5 MPa.At this time, 11.3 g of nickel powder as seed crystals and 0.5 g/L ofsodium polyacrylate as a dispersant were added to perform the reaction.Incidentally, the pH of the post-reduction liquid was decreased to 3.8.

After completion of the reaction, the reacted slurry was taken out fromthe reaction container, the generated nickel powder was recovered bysolid-liquid separation, and the quantity thereof was measured. As aresult, it was confirmed that 97.7% of nickel contained in the suppliednickel ammine complex aqueous solution can be recovered as a metallicnickel powder.

Example 4

The treatment from the first step to the third step was performed usingthe same method as in Example 3 to obtain 1 L of nickel ammine complexaqueous solution.

Subsequently, 15 mL of ammonia water having a concentration of 25% wasadded to the obtained nickel ammine complex aqueous solution, and theaqueous solution thereof was charged in a high temperature and highpressure reaction container. Then, similarly to the reduction step ofExample 3, 11.3 g of nickel powder as seed crystals and 0.5 g/L ofsodium polyacrylate as a dispersant was added and the reaction wasperformed for 1 hour by supplying hydrogen gas under the conditionsincluding a temperature of 185° C. and an internal pressure of 3.5 MPa.Incidentally, the pH of the post-reduction liquid was 7.7.

After completion of the reaction, the reacted slurry was taken out fromthe reaction container, the generated nickel powder was recovered bysolid-liquid separation, and the quantity thereof was measured. As aresult, it was confirmed that 99.3% of nickel contained in the suppliednickel ammine complex aqueous solution can be recovered as a metallicnickel powder.

Incidentally, from the comparison with the result of Example 3, it wasconfirmed that the nickel reduction rate is improved by adding a smallamount of ammonia to the nickel ammine complex aqueous solution as atarget for the hydrogen reduction to suppress a decrease in pH.

1. A nickel powder manufacturing method, the method comprising: a firststep for generating a post-neutralization slurry containing nickelhydroxide by mixing a nickel sulfate aqueous solution and a neutralizingagent; a second step for causing a complex-forming reaction by mixing anammonium sulfate aqueous solution with the post-neutralization slurryobtained in the first step and obtaining a post-complexation slurrycontaining a nickel ammine complex aqueous solution; and a reductionstep for obtaining nickel powder and a post-reduction solution bybringing hydrogen gas into contact with the nickel ammine complexaqueous solution obtained in the second step.
 2. The nickel powdermanufacturing method according to claim 1, wherein in the second step,the post-reduction solution obtained in the reduction step is used asthe ammonium sulfate aqueous solution to be mixed with thepost-neutralization slurry.
 3. The nickel powder manufacturing methodaccording to claim 1, the method further comprising a third step forsubjecting the post-complexation slurry obtained in the second step tosolid-liquid separation into a nickel ammine complex aqueous solutionand a post-complexation sediment and supplying the nickel ammine complexaqueous solution to the reduction step.
 4. The nickel powdermanufacturing method according to claim 1, wherein in the first step,slaked lime and/or sodium hydroxide is used as the neutralizing agent.5. The nickel powder manufacturing method according to claim 1, whereinin the reduction step, the nickel powder is obtained by adding ammoniawater to the nickel ammine complex aqueous solution and then bringingthe hydrogen gas into contact with the nickel ammine complex aqueoussolution.
 6. The nickel powder manufacturing method according to claim2, the method further comprising a third step for subjecting thepost-complexation slurry obtained in the second step to solid-liquidseparation into a nickel ammine complex aqueous solution and apost-complexation sediment and supplying the nickel ammine complexaqueous solution to the reduction step.
 7. The nickel powdermanufacturing method according to claim 2, wherein in the first step,slaked lime and/or sodium hydroxide is used as the neutralizing agent.8. The nickel powder manufacturing method according to claim 3, whereinin the first step, slaked lime and/or sodium hydroxide is used as theneutralizing agent.
 9. The nickel powder manufacturing method accordingto claim 6, wherein in the first step, slaked lime and/or sodiumhydroxide is used as the neutralizing agent.
 10. The nickel powdermanufacturing method according to claim 2, wherein in the reductionstep, the nickel powder is obtained by adding ammonia water to thenickel ammine complex aqueous solution and then bringing the hydrogengas into contact with the nickel ammine complex aqueous solution. 11.The nickel powder manufacturing method according to claim 3, wherein inthe reduction step, the nickel powder is obtained by adding ammoniawater to the nickel ammine complex aqueous solution and then bringingthe hydrogen gas into contact with the nickel ammine complex aqueoussolution.
 12. The nickel powder manufacturing method according to claim4, wherein in the reduction step, the nickel powder is obtained byadding ammonia water to the nickel ammine complex aqueous solution andthen bringing the hydrogen gas into contact with the nickel amminecomplex aqueous solution.
 13. The nickel powder manufacturing methodaccording to claim 6, wherein in the reduction step, the nickel powderis obtained by adding ammonia water to the nickel ammine complex aqueoussolution and then bringing the hydrogen gas into contact with the nickelammine complex aqueous solution.
 14. The nickel powder manufacturingmethod according to claim 7, wherein in the reduction step, the nickelpowder is obtained by adding ammonia water to the nickel ammine complexaqueous solution and then bringing the hydrogen gas into contact withthe nickel ammine complex aqueous solution.
 15. The nickel powdermanufacturing method according to claim 8, wherein in the reductionstep, the nickel powder is obtained by adding ammonia water to thenickel ammine complex aqueous solution and then bringing the hydrogengas into contact with the nickel ammine complex aqueous solution. 16.The nickel powder manufacturing method according to claim 9, wherein inthe reduction step, the nickel powder is obtained by adding ammoniawater to the nickel ammine complex aqueous solution and then bringingthe hydrogen gas into contact with the nickel ammine complex aqueoussolution.